Blends of linear and branched neodymium-catalyzed rubber formulations for use in golf balls

ABSTRACT

The invention relates to golf ball formulations formed from blends of linear and branched polybutadienes catalyzed with neodymium that have improved properties and processing characteristics. Golf ball components may be formed from the blends to provide high coefficient of restitution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/084,274, filed Nov. 19, 2013, now U.S. Pat. No. 9,205,307,which is a continuation of U.S. patent application Ser. No. 12/910,914,filed Oct. 25, 2010, now U.S. Pat. No. 8,586,678, the entire disclosuresof which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to rubber compositions for use in golfballs, more particularly to compositions that include blends ofpolybutadiene rubbers having improved properties and processingcharacteristics.

BACKGROUND OF THE INVENTION

Conventional golf balls, solid or wound, typically have at least onecore layer and at least one cover layer. Two-piece balls having a solidconstruction are popular with golfers because they provide a verydurable ball with high initial velocity resulting in longer flightdistance. Due to the rigidity of the materials used, however, the ballshave a “hard” feel when struck with a club and a relatively low spinrate that makes them difficult to control, particularly on shorterapproach shots.

Wound balls, i.e., spherical solid rubber or liquid center with atensioned elastomeric thread wound thereon, are preferred by somegolfers for a softer feel and higher spin enabling better control in andaround the green. Wound balls typically travel a shorter distance,however, when struck as compared to a two piece ball. Moreover, as aresult of their more complex structure, wound balls generally require alonger time to manufacture and are more expensive to produce than aconventional two piece ball.

Solid cores, used in wound or solid golf balls, are generally formed ofa polybutadiene composition. In addition to one-piece cores, solid corescan also contain a number of outer layers, such as in a dual core golfball. Covers, for solid or wound balls, are generally formed of ionomerresins, balata, polyurea, or polyurethane, and can consist of a singlelayer or include one or more layers, e.g., a dual cover with an innerand outer cover layer, and optionally at least one intermediate layerdisposed about the core.

The core of solid golf balls is the “engine” of the ball, providing thevelocity required for good distance. However, a core that is too hardcan result in a golf ball that provides poor feel. Manufacturers areconstantly experimenting with various core compositions andconstructions in an effort to optimize both feel and distance. Mostconventional solid cores comprise polybutadiene rubber or some modifiedform thereof, which provides the primary source of resiliency for thegolf ball.

Polybutadiene rubber core compositions still have room for improvementin resilience, which is determined by coefficient of restitution(“COR”). As would be appreciated by those skilled in the art of golfball manufacturing, the COR along with angle of trajectory (i.e., launchangle) and club head speed determine the distance a golf ball willtravel when hit by a golf club. One way to measure the COR is to propela ball at a given speed against a hard massive surface and measure itsincoming and outgoing velocity. The COR is the ratio of the outgoingvelocity to the incoming velocity and is expressed as a decimal betweenzero and one. There is no United States Golf Association limit on theCOR of a golf ball, but the initial velocity of the golf ball cannotexceed 250+/−5 feet/second. As a result, the industry goal for initialvelocity is 255 feet/second, and the industry strives to maximize theCOR without violating this limit.

In general, polybutadiene rubbers of high molecular weight (high Mooneyviscosity) have better resilience than polybutadiene rubbers of lowmolecular weight (low Mooney viscosity). However, as the molecularweight increases, the milling and processing properties of thepolybutadiene rubber deteriorate. Polybutadiene rubber catalyzed withlanthanide series elements, such as neodymium, tends to be linear andnarrow in polydispersity (closer to 1.0). The linearity and narrowpolydispersity allows high-molecular weight neodymium-catalyzedpolybutadiene rubber (“Nd-BR”) to provide improved resilience, butcauses problems in extrusion processes and storage difficulties such ascold flow. In comparison to Nd-BR, polybutadiene rubber catalyzed withcobalt and/or nickel (“Co-BR, Ni-BR”) is typically more branched and haswider polydispersity (distant from 1.0). However, while the branchingcharacteristic facilitates processing, the wide polydispersity andbranching generally gives low resilience.

Attempts to improve golf ball COR by using various blends ofpolybutadiene rubber in core compositions include, among others, U.S.Pat. Nos. 4,683,257; 4,931,376; 4,955,613; 4,984,803; 5,082,285;6,139,447; 6,277,920; 6,315,684; and 6,774,187.

While advances have been made, there remains a need in the golf ballmanufacturing art to provide compositions with improved properties andprocessability that are useful in golf ball components and, morespecifically, golf ball core components. Advantageously, thecompositions of the present invention provide enhanced processingcharacteristics without sacrificing resilience in the resulting golfballs.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball including a core and acover, wherein the core is formed from a blend including: a linearpolybutadiene formed with a neodymium catalyst having a first Mooneyviscosity of from about 30 to about 100; and a branched polybutadieneformed with a neodymium catalyst having a second Mooney viscosity offrom about 20 to about 90, wherein the second Mooney viscosity is lessthan the first Mooney viscosity. In one embodiment, the second Mooneyviscosity is about 30 to about 75. In one embodiment, the linearpolybutadiene has a higher Mooney Stress Relaxation than the branchedpolybutadiene. In another embodiment, the blend may further include acobalt-, lithium-, titanium-, or nickel-catalyzed polybutadiene, or acombination thereof.

In this aspect of the invention, the branched polybutadiene may have aMooney viscosity of from about 30 to about 75. In one embodiment, thesecond Mooney viscosity is about 35 to about 50. For example, the secondMooney Viscosity may range from about 40 to about 45. In addition, thebranched polybutadiene may have a solution viscosity to Mooney Viscosityratio of about 4 or less and the linear polybutadiene may have asolution viscosity to Mooney Viscosity ratio of greater than about 5. Inone embodiment, the solution viscosity to Mooney Viscosity ratio of thelinear polybutadiene is at least about 2 times greater than the solutionviscosity to Mooney Viscosity ratio of the branched polybutadiene. Inone embodiment, the solution viscosity to Mooney Viscosity ratio is from2 to about 4. For example, the solution viscosity to Mooney Viscosityratio may range from about 3.6 to about 3.75. In another embodiment, thelinear polybutadiene has a first polydispersity and the branchedpolybutadiene has a second polydispersity greater than the firstpolydispersity.

The golf ball may also include one or more layers disposed between thecore and the cover. For example, in one embodiment, the ball includes anintermediate layer disposed between the cover and the core.

The present invention also relates to a golf ball including a core and acover wherein a portion of the golf ball is formed from a blendincluding: a linear polybutadiene formed with a neodymium catalysthaving a first polydispersity; and a branched polybutadiene formed witha neodymium catalyst having a second polydispersity greater than thefirst polydispersity, wherein the second polydispersity is greater thanabout 2.

The present invention also relates to a golf ball including a core, acover, and an intermediate layer disposed between the cover and thecore, wherein a portion of the golf ball is formed from a blendincluding: a linear polybutadiene formed with a neodymium catalysthaving a first polydispersity and a first Mooney viscosity; and abranched polybutadiene formed with a neodymium catalyst having a secondpolydispersity greater than the first polydispersity and a second Mooneyviscosity less than the first Mooney viscosity, wherein the secondpolydispersity is greater than about 2, and wherein the second Mooneyviscosity is of from about 35 to about 50.

In one embodiment, the linear polybutadiene has a first Mooney StressRelaxation and the branched polybutadiene has a second Mooney StressRelaxation, and wherein the second Mooney Stress Relaxation is less thanthe first Mooney Stress Relaxation. In another embodiment, the firstpolydispersity is less than about 3. In yet another embodiment, thelinear polybutadiene has a solution viscosity to Mooney Viscosity ratiothat is at least 2 times greater than the solution viscosity to MooneyViscosity ratio of the branched polybutadiene. In still anotherembodiment, the first Mooney viscosity is from about 30 to about 100. Instill another embodiment, the core includes a center and at least oneouter core layer, and wherein at least one of the center or the outercore includes the blend. In another embodiment, the cover includespolyurethane, polyurea, or a combination thereof.

The present invention is also directed to a golf ball including a coreand a cover, wherein the core includes a blend including: a linearpolybutadiene formed with a neodymium catalyst having a firstpolydispersity and a first solution viscosity to Mooney Viscosity ratio;and a branched polybutadiene formed with a neodymium catalyst having asecond polydispersity greater than the first polydispersity and a secondsolution viscosity to Mooney Viscosity ratio less than the firstsolution viscosity to Mooney Viscosity ratio. In one embodiment, thesecond solution viscosity to Mooney Viscosity ratio may range from about2 to about 4. In another embodiment, the first solution viscosity toMooney Viscosity ratio ranges from about 5 to about 12.

In this aspect of the invention, the cover may also include a thermosetmaterial. In another embodiment, the ball may include an intermediatelayer formed from a thermoplastic material. In yet another embodiment,the ratio of weight percentage of the branched polybutadiene to thelinear polybutadiene is at least about 60:40.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention can be ascertained fromthe following detailed description that is provided in connection withthe drawing(s) described below:

FIG. 1 is a cross-sectional view of a two-piece golf ball having a coverand a core according to the invention.

FIG. 2 is a cross-section of a golf ball having an intermediate layerbetween a cover and a center according to the invention.

FIG. 3 is a cross-section of a golf ball having a large core and a dualcover layer according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “about” is used in connection with one or morenumbers or numerical ranges, should be understood to refer to all suchnumbers, including all numbers in a range.

The present invention is directed toward blends of branched Nd-BR andlinear Nd-BR that may be used in golf ball components. A variety of golfball constructions, i.e., one-piece, two-piece, or multilayer balls, arepossible for use in the present invention. As used herein, the term“multilayer” refers to golf balls having at least two layers, whichincludes wound balls and balls with multiple core, intermediate, andcover layers.

The compositions of the invention include a blend of two or morepolybutadiene rubber (“BR”) components, both formed with a lanthanideseries catalyst. In particular, a neodymium (“Nd”) catalyst is apreferred lanthanide series catalyst for both polybutadienes. Forexample, the blend may include a long-chain branched polybutadienerubber formed with a neodymium catalyst (“branched Nd-BR”) and a linearpolybutadiene rubber formed with a neodymium catalyst (“linear Nd-BR”).Both the linear and branched Nd-BR rubbers preferably have a cis-1,4content of at least about 95 percent. In one embodiment, at least one ofthe linear and branched Nd-BR rubbers has a cis-1,4 content of at leastabout 96 percent. In still another embodiment, at least one of thelinear and branched Nd-BR rubbers has a cis-1,4 content of at leastabout 98 percent. The blend may optionally contain cobalt, lithium,titanium, or nickel catalyzed polybutadienes.

As will be understood by those skilled in the art, polymers such aspolybutadiene may be characterized according to various definitions ofmolecular weight. In this regard, the branched Nd-BR may have a weightaverage molecular weight (M_(w)) that ranges from about 200,000 to about600,000. In one embodiment, the M_(w) of the branched Nd-BR ranges fromabout 250,000 to about 450,000. In another embodiment, the branchedNd-BR ranges from about 300,000 to about 400,000. The number averagemolecular weight (M_(n)) of the branched Nd-BR may range from about50,000 to about 400,000, preferably about 80,000 to about 300,000, andmore preferably about 85,000 to about 200,000.

A common indicator of the degree of molecular weight distribution of apolymer is its polydispersity, defined as the ratio of weight averagemolecular weight (M_(w)) to number average molecular weight (M_(n)).Polydispersity also provides an indication of the extent to which thepolymer chains share the same degree of polymerization. If thepolydispersity is 1.0, then all polymer chains must have the same degreeof polymerization. Since M_(w) is always equal to or greater than M_(n),polydispersity, by definition, is equal to or greater than 1.0. Linearpolymers tend to have a polydispersity that is close to 1.0. Incontrast, a branched polymer may have a polydispersity that is muchgreater than 1.

For example, the polydispersity of the linear Nd-BR may be less thanabout 3. In one embodiment, the linear Nd-BR has a polydispersity ofabout 1.5 to about 2.8. In another embodiment, polydispersity of thelinear Nd-BR ranges from about 1.7 to about 2.5. In still anotherembodiment, the polydispersity of the linear Nd-BR ranges from about 1.8to about 2.3. In contrast, the polydispersity of the branched Nd-BR maybe greater than about 2. In one embodiment, the polydispersity of thebranched Nd-BR is greater than about 3. In another embodiment, thebranched Nd-BR has a polydispersity of about 3.5 or greater, preferablyabout 3.5 or greater. In still another embodiment, the branched Nd-BRhas a polydispersity of about 4 or greater, preferably about 4.25 orgreater. In another embodiment, the polydispersity of the branched Nd-BRis greater than about 5.

Without being bound to any particular theory, it is believed that a widepolydispersity generally results in a low resilience. As discussedabove, a convenient method for expressing the resilience of a polymer isthrough Coefficient of Restitution (“COR”). The Nd-BR blends of thepresent invention result in a golf ball component with a COR value ofgreater than about 0.78. Preferably, the COR of the golf ball componentis greater than about 0.79. In one embodiment, golf ball component has aCOR of about 0.8 or greater.

As discussed above, Mooney viscosity is related to the molecular weightof a polymer. For example, as the molecular weight increases, the Mooneyviscosity increases. The measurement of Mooney viscosity is definedaccording to ASTM D-1646. The polybutadienes of the present inventionpreferably have a Mooney viscosity that is less than about 100. In oneembodiment, the linear Nd-BR has a Mooney viscosity between about 30 andabout 100. Preferably, the linear Nd-BR has a Mooney viscosity betweenabout 40 and about 80. More preferably, the Mooney viscosity for thelinear Nd-BR is between about 45 and about 60. The branched Nd-BRpreferably has a lower Mooney viscosity than the linear polybutadiene.In one embodiment, the branched Nd-BR has a Mooney viscosity betweenabout 20 and about 90. Preferably the branched Nd-BR has a Mooneyviscosity between about 30 and about 75. More preferably, the branchedNd-BR has a Mooney viscosity between about 35 and about 50. For example,the branched Nd-BR may have a Mooney viscosity between about 40 andabout 45. In an exemplary embodiment, the branched Nd-BR has a Mooneyviscosity of about 44.

The polybutadienes of the present invention are also definable by theirrespective solution viscosity (SV) values. In one embodiment, thebranched Nd-BR of the present invention has a solution viscosity of fromabout 155 to about 170. In another embodiment, the branched Nd-BR has asolution viscosity of from about 159 to about 165.

As would be understood by those skilled in the art, polymers with a highsolution viscosity (SV) with respect to the Mooney viscosity (MV)experience cold flow problems and suffer a disadvantage inprocessability. Therefore, it may be desirable from a processingstandpoint to reduce the ratio of solution viscosity to Mooney viscosity(SV/MV). Linear polymers may have a high SV/MV ratio, which as mentionedabove, may contribute to processing problems. For example, the linearNd-BR may have a solution viscosity to Mooney viscosity ratio of betweenabout 5 and about 15. In one embodiment, the SV/MV ratio for the linearNd-BR is between about 5 and about 12. In another embodiment, the linearNd-BR has a SV/MV ratio that ranges from about 5 to about 10. In stillanother embodiment, the SV/MV ratio of the linear Nd-BR ranges fromabout 5 to about 7.

By contrast, the branched Nd-BR may have a SV/MV that is about 4 orless. In one embodiment, the SV/MV ratio of the branched Nd-BR is lessthan about 4. For example, the branched Nd-BR may have a SV/MV ratiothat is about 3.8 or less, 3.75 or less, or about 3.6 or less. In oneembodiment, the SV/MV ratio ranges from about 3.6 to about 3.8. Inanother embodiment, the SV/MV ratio is about 3.5 or less. In stillanother embodiment, the SV/MV ratio of the branched Nd-BR may be about 3or less. In another embodiment, the SV/MV ratio for the branched Nd-BRranges from about 1.8 to about 4, preferably about 2 to about 4. In yetanother embodiment, the branched Nd-BR may have a SV/MV ratio from about3.6 to about 3.75, preferably from about 3.6 to about 3.65.

In particular, as shown in Table 1 below, both the linear and branchedNd-BR that are included in the blends of the present invention haveSV/MV ratio values that are greater than the SV/MV ratio of a branchedcobalt catalyzed polybutadiene.

TABLE I SV/MV Branched Co-BR 1.3 1.4 1.7 Linear Nd-BR 5.9 6.3 6.6Branched Nd-BR 2.1 3.2 3.6 3.63 3.75 3.8As shown in Table I, branched Nd-BR has a SV/MV ratio that is lower thanlinear Nd-BR. However, as discussed above, since linear Nd-BR has arelatively lower polydispersity than branched Nd-BR, blends of branchedand linear Nd-BR offer the processability of branched Nd-BR combinedwith the resilience of linear Nd-BR.

In one embodiment, the SV/MV ratio of the linear Nd-BR is at least about2 times greater than the SV/MV ratio of the branched Nd-BR. In anotherembodiment, the SV/MV ratio of the linear Nd-BR is at least about 2.5times greater than the SV/MV ratio of the branched Nd-BR. In yet anotherembodiment, the SV/MV ratio of the linear Nd-BR is at least about 3times greater than the SV/MV ratio of the branched Nd-BR.

Another method of determining the processability of a polymer is tomeasure the Mooney Stress Relaxation (MSR). A high MSR may result inprocessing problems, such as die swell and extrudate or calendered sheetshrinkage. The MSR of the linear Nd-BR may range from about 0.45 toabout 0.75, preferably about 0.50 to about 0.70. The MSR of the branchedNd-BR may range from about 0.45 to about 0.75, preferably about 0.45 toabout 0.70. Table II demonstrates the MSR values for several linearNd-BR and branched Nd-BR samples, as well as for branched Co-BR.

TABLE II MSR Branched Co-BR 0.34 0.37 0.41 Linear Nd-BR 0.50 0.57 0.69Branched Nd-BR 0.46 0.50 0.68As shown in the data above, the linear Nd-BR has a higher MSR than thebranched Nd-BR, but both have a higher MSR than the short-chain branchedcobalt grades that are currently used in blends with linearneodymium-catalyzed polybutadienes. In this respect, the blends of theinvention are believed to achieve a better balance of resilience,millability, ease of extrusion, and resistance to cold flow thanconventional blends of linear polybutadiene and short-chain branchedcobalt-catalyzed polybutadiene.

In one embodiment, the ratio of MSR of the linear Nd-BR to the branchedNd-BR is greater than 1.0. For example, the ratio of the linear Nd-BRMSR to the branched Nd-BR MSR ranges from about 1.0 to about 1.2. Inanother embodiment, the ratio of the linear Nd-BR MSR to the branchedNd-BR MSR ranges from about 1.01 to about 1.15.

According to one aspect of the present invention, the ratio of weightpercentage in the blend of the branched Nd-BR to linear Nd-BR ispreferably at least about 51:49, more preferably at least about 60:40,and most preferably at least about 75:25.

In an alternative embodiment, the blend includes more linear Nd-BR andless branched Nd-BR. In one embodiment, the linear Nd-BR to branchedNd-BR ratio of weight percentage is preferably at least about 51:49,more preferably at least about 60:40, and most preferably at least about75:25. In another embodiment, the linear Nd-BR to branched Nd-BR ratioof weight percentage is about 80:20, more preferably 90:10, and mostpreferably 95:5.

Methods for the preparation of a linear Nd-BR are known in the art anddescribed in U.S. Pat. No. 6,774,187, which is incorporated by referencein its entirety. In particular, a polybutadiene rubber that is catalyzedwith lanthanide series catalysts may be prepared by polymerizingbutadiene monomer in the presence of catalysts comprising a lanthanideseries element and compound, an organoaluminum compound, a Lewis base,and optionally, a Lewis acid. In this regard, it is preferable that thelanthanide element is neodymium. The Lewis bases serve to convert thelanthanide element into complexes, and acetylacetone and ketone alcoholsand the like may be used for this purpose. In the synthesis of Nd-BR,the Nd catalysts may be used as solution in a suitable solvent such asn-hexane, cyclohexane, n-heptane, toluene, xylene, benzene, etc. orcarried on suitable carriers such as silica, magnesia, and magnesiumchloride. The polymerization temperature typically ranges from about−30° C. to about 150° C., preferably from about 10° C. to about 80° C.The polymerization pressure may vary depending on other conditions.Examples of commercially available Nd-BR for use in the preparation ofthe linear Nd-BR include, but are not limited to, Buna® CB21, CB22 andCB23, available from Lanxess Corporation, Neodene 40 and Neodene 45,available from Karbochem, and BR51, T700 and BR730, available from JSRCorporation.

Without being bound to any particular theory, a long-chain branchedNd-BR may be produced through a “Mooney Jump Reaction”, also known as a“molecular weight jumping” reaction. A “Mooney Jump Reaction” is awell-known process for increasing the degree of branching of a polymer,which results in an increase in molecular weight. A non-limiting exampleof a “Mooney Jump Reaction” is depicted below.

One non-limiting example of a commercially available branched Nd-Brsuitable for use in the present invention is Buna® CB25, which isavailable from Lanxess Corporation. Other non-limiting examples ofcommercially available branched Nd-Br suitable for use in the presentinvention include Buna® CB24-Orange, Buna® CB24-Dormagen, and Buna® CB728T, which are also available from Lanxess Corporation. In this aspect,suitable branched Nd-Br for use in the present invention include thosehaving a high cis-1,4 content, e.g., at least 96 percent.

In addition to the previously discussed components of the blends of thepresent invention, the compositions of the invention may include otherspecies of butadiene rubber, as well as natural rubber, balata,gutta-percha, synthetic polyisoprene, styrene-butadiene rubber,styrene-propylene-diene rubber, chloroprene rubber, acrylonitrilerubber, acrylonitrile-butadiene rubber, ethylene-propylene rubber,ethylene-propylene-diene terpolymer, and mixtures thereof. For example,the blends of the present invention may also include styrene-butadienerubber (SBR) in an amount of about 1 to about 30 parts per hundred. Inone embodiment, the blends of the invention include about 5 to about 20parts per hundred of SBR. Similarly, the blends of the invention mayalso include about 1 to about 30 parts per hundred of natural rubber(NR), polyisoprene rubber (PIP), butyl rubber, or mixtures thereof. Inone embodiment, the blends of the invention also include about 5 toabout 20 parts per hundred NR, PIP, butyl rubber, or combinationsthereof.

In addition, the COR of the golf ball component formed from thecompositions of the invention may be reduced by the addition of certaintypes of rubber to the blend. For example, styrene-butadiene rubber,natural rubber, polyisoprene, butyl or halogenated butyl rubber, lowercis-content butadiene rubber, high-trans or high-vinyl content butadienerubber, and similar rubbers may be added to the mixture as needed toadjust the COR.

Cross-Linking Agent

One conventional adduct to the blend is a reactive co-agent thatcrosslinks (i.e., vulcanizes) the rubber. To prevent water absorption tothe core and enhance the durability of the golf ball, the amount ofco-agent is minimized to preferably less than about 10 parts per hundred(“phr”) by weight of the blend, more preferably less than about 5 phr,and most preferably about 0 phr (no co-agent).

Alternatively, a moderately hard component may be achieved using theco-agent in an amount between about 10 phr and about 50 phr by weight ofthe BR blend. Furthermore, the core may be very hard and dense when atleast about 50 phr of the co-agent is incorporated into the core. Theco-agent is preferably a salt of an unsaturated carboxylic acid havingabout 3 to 8 carbon atoms; an unsaturated vinyl compound; apolyfunctional monomer; phenylene bismaleimide; or a mixture thereof.

In one aspect of the invention, the blends also incorporate at least onereactive co-agent to enhance the hardness. A suitable co-agent for usein this aspect may be formed from an unsaturated carboxylic acid,preferably an α,β-ethylenically unsaturated carboxylic acid having about3 to 8 carbon atoms, such as methacrylic, acrylic, itaconic, sorbic,cinnamic and crotonic acid. Suitable counterions include, but are notlimited to, quaternary phosphonium or ammonium cations such astetraalkyl phosphonium, and metal cations such as sodium, lithium,potassium, magnesium, calcium, zinc, barium, aluminum, tin, zirconium,nickel and cadmium. Zinc, magnesium and cadmium are preferred as themetal cations.

Other co-agents may comprise unsaturated vinyl compounds includingwithout limitation N,N′-m-phenylene dimaleimide (available as Vanax® MBMfrom R. T. Vanderbilt); trimethylolpropane trimethacrylate (Sartomer®SR-350 from Sartomer); triallyl trimellitate (Triam® 705 from WakoChemicals); triallylisocyanurate (Taic® from Nippon Kasei Chemical);acrylate-terminated liquid polybutadiene (PolyBD® 300 from Elf AtochemN.A.); and mixtures thereof. In addition, poly-functional monomers,phenylene bismaleimide and sulfur may also be used as the co-agent.

In one embodiment, the co-agent is a mono-(meth)acrylic acid ordi-(meth)acrylic acid metal salt, wherein the cation is zinc, magnesium,calcium, or mixtures thereof. As used herein, the term “(meth)acrylic”includes both methacrylic and acrylic. For example, the co-agent may bezinc diacrylate (“ZDA”), zinc dimethacrylate (“ZDMA”), or mixturesthereof. Of the common acrylate cross-linkers, ZDA has generally beenfound to produce golf balls with greater initial velocity than ZDMA,therefore, the former may be preferable to achieve a specific initialvelocity. The ZDA can be of various grades of purity. For the purposesof this invention, the lower the quantity of zinc stearate present inthe ZDA the higher the ZDA purity. Thus, ZDA containing less than about10 percent zinc stearate is preferable. In one embodiment, ZDAcontaining between about 4 percent and about 8 percent zinc stearate isemployed. The co-agent may be present in an amount from about 0 to about50 phr by weight of the blend.

Free Radical Source(s)

Conventionally, a free radical initiator is used to promote thecrosslink reaction between the reactive co-agent and the polybutadienerubber. The free radical initiators included in the core compositionsherein may be any known polymerization initiators that produce freeradicals during the curing cycle. Suitable initiators include peroxides,persulfates, azo compounds and hydrazides.

Examples of the peroxides for the purposes of the present inventioninclude dicumyl peroxide; n-butyl-4,4-di(t-butylperoxy)-valerate;1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane;α,α′-bis(t-butylperoxy)-diisopropylbenzene;2,5-dimethyl-2,5-di(t-butylperoxy)hexane; di-t-butyl peroxide; di-t-amylperoxide; di(2-t-butyl-peroxyisopropyl)benzene peroxide; laurylperoxide; benzoyl peroxide; t-butyl hydroperoxide; and mixtures thereof.

Preferably, the peroxide initiator is dicumyl peroxide having anactivity between about 40 percent and about 100 percent. The initiatormay be present in the blend in an amount ranging between about 0.05 phrand about 15 phr by weight of the blend. For example, in one embodiment,the amount of the initiator ranges between about 0.1 phr and about 5phr, and most preferably between about 0.25 and about 1.5 phr. Those ofordinary skill in the art will understand that the total amount ofinitiators used will vary depending on the specific end product desiredand the particular initiators employed.

Alternatively, sulfur-based curing agents with optional accelerators maybe used in combination with or in replacement of the peroxide initiatorsto crosslink the BR, as described in U.S. Pat. No. 6,695,718, thedisclosure of which is incorporated herein by reference in its entirety.Other useful initiators will be readily apparent to one of ordinaryskill in the art. The initiator may alternatively or additionally be oneor more of electron beams; gamma radiation; infrared radiation;ultra-violet radiation; X-ray radiation; or any other high-energyradiation source capable of generating free radicals. It should befurther understood that heat often facilitates initiation of thegeneration of free radicals.

Filler(s)

Fillers may be added to one or more portions of the golf ball. In oneembodiment, at least one filler is added to the blend. Fillers typicallyinclude processing aids or compounds to affect rheological and mixingproperties, the specific gravity (i.e., density-modifying fillers), themodulus, the tear strength, reinforcement, and the like. The fillers aregenerally inorganic, and suitable fillers include numerous metals, metaloxides and salts, such as zinc oxide and tin oxide, as well as bariumsulfate, zinc sulfate, calcium carbonate, zinc carbonate, bariumcarbonate, clay, tungsten, tungsten carbide, an array of silicas,regrind (recycled core material typically ground to about 30 meshparticle), high-Mooney-viscosity rubber regrind, and mixtures thereof.

Fillers may also include various foaming agents or blowing agents whichmay be readily selected by one of ordinary skill in the art. Foamedpolymer blends may be formed by blending blowing agent(s) with polymermaterial, as is well known by those of ordinary skill in the art.Polymeric, ceramic, metal, or glass microspheres, or combinationsthereof, may be used to adjust the density or other properties of agiven layer, and such microspheres may be solid or hollow, and filled orunfilled. Fillers are typically also added to one or more portions ofthe golf ball to modify the density thereof to conform to uniform golfball standards. Fillers may also be used to modify the weight of thecenter or at least one additional layer for specialty balls, e.g., alower weight ball is preferred for a player having a low swing speed.

The compositions of the present invention may additionally comprise anyother suitable and compatible modifying ingredients including, but notlimited to, metal oxides, fatty acids, and diisocyanates. For example,metal oxides such as zinc oxide and/or magnesium oxide may be added asactivators for the BR. Fatty acids or metallic salts of fatty acids suchas stearic, palm itic, oleic and linoleic acids may be included asmoldability and processing additives. Polymeric diisocyanates such as4,4′-diphenylmethane diisocyanate and other polyfunctional isocyanatesmay also be incorporated in the rubber compositions as moisturescavengers.

Other additives suitable for the core compositions, including stablefree radicals; free radical scavangers; scorch retarders; cis-to-transcatalysts; density fillers; nanofillers; dispersing agents; foamingagents; antioxidants; chain-transfer agents; stabilizers; processingaids; processing oils; plasticizers; dyes and pigments; as well as otheradditives well known to the skilled artisan, may also be used in thepresent invention in amounts sufficient to achieve the purpose for whichthey are typically used.

Antioxidant

The rubber composition optionally contains one or more antioxidants.Antioxidants are compounds that can inhibit or prevent the oxidativedegradation of the rubber. Some antioxidants also act as free radicalscavengers; thus, when antioxidants are included in the rubbercomposition, the amount of initiator agent used may be as high or higherthan the amounts disclosed herein. Suitable antioxidants include, forexample, dihydroquinoline antioxidants, amine type antioxidants, andphenolic type antioxidants.

Golf Ball Construction

As discussed briefly above, the compositions of the present inventionmay be used with any type of ball construction including, but notlimited to, one-piece, two-piece, three-piece, and four-piece designs, adouble core, a double cover, an intermediate layer(s), a multilayercore, and/or a multi-layer cover depending on the type of performancedesired of the ball. That is, the compositions of the invention may beused in a core, an intermediate layer, and/or a cover of a golf ball,each of which may have a single layer or multiple layers. In oneembodiment, the compositions of the invention are formed into a corelayer.

As used herein, the term “multilayer” means at least two layers. Forinstance, the core may be a one-piece core or a multilayer core, i.e., acore that has an innermost component with an additional core layer oradditional core layers disposed thereon. As used herein, the terms“core” and “center” are generally used interchangeably to reference theinnermost component of the ball. In some embodiments, however, the term“center” is used when there are multiple core layers, i.e., a center andan outer core layer.

When the golf ball of the present invention includes an intermediatelayer, which may also include more than one layer, this layer may beincorporated with a single or multilayer cover, a single or multi-piececore, with both a single layer cover and core, or with both a multilayercover and a multilayer core. The intermediate layer may be also bereferred to as an inner cover layer or outer core layer, or any otherlayer(s) disposed between the inner core and the outer cover of a golfball.

Referring to FIG. 1, a golf ball 2 of the present invention can includea center 4 and a cover 6 surrounding the center 4. Referring to FIG. 2,a golf ball 8 of the present invention can include a center 10, a cover14, and at least one intermediate layer 12 disposed between the coverand the center. In one embodiment, the cores 4 and/or 14 may be formedfrom the composition of the invention. Each of the layers in FIG. 1 or 2may include more than one layer, i.e., the golf ball can be aconventional three-piece wound ball, a two-piece ball, a ball having amulti-layer core and an intermediate layer or layers, etc. Also, FIG. 3shows a golf ball 16 of the present invention including a large core 18,a cover 22, and an inner cover layer 20. In one embodiment, the core 18includes a center and an outer core layer. The core 18 may be formedfrom the composition of the invention. In one embodiment, the cover 22is formed from a polyurethane or polyurea material.

Golf Ball Core Layer(s)

The core or core layer(s) may be formed from the compositions of theinvention. For example, a core formed from the composition of theinvention may be covered with a castable thermoset or injection moldablethermoplastic material or any of the other cover materials discussedbelow. The core may have a diameter of about 1.5 inches to about 1.62inches and the cover layer thickness may range from about 0.03 inches toabout 0.06 inches. The core compression preferably ranges from about 30to about 120 atti and the overall ball compression is about 50 to about110. In one embodiment, the PGA compression of a core formed from thecomposition of the invention is about 5 PGA to about 40 PGA. In anotherembodiment, the core has a PGA compression value of about 10 to about40, preferably about 15 to about 20. The overall ball has a PGAcompression value of about 20 to about 80, preferably about 25 to about65, and more preferably about 30 to about 45. For example, the overallball may have a PGA compression of about 30 to about 35. In oneembodiment, the PGA compression of the overall ball is about 35 to about45. In another embodiment, the PGA compression of the overall ball isabout 35 to about 40.

When not formed from the compositions of the invention, any corematerial known to one of ordinary skill in that art is suitable for usein the golf balls of the invention. In particular, the core may besolid, semi-solid, hollow, fluid-filled or powder-filled, one-piece ormulti-component cores. As used herein, the term “fluid” includes aliquid, a paste, a gel, a gas, or any combination thereof; the term“fluid-filled” includes hollow centers or cores; and the term“semi-solid” refers to a paste, a gel, or the like.

Suitable core materials include thermoset materials, such as rubber,styrene butadiene, polybutadiene, isoprene, polyisoprene,trans-isoprene, as well as thermoplastics such as ionomer resins,polyamides or polyesters, and thermoplastic and thermoset polyurethaneelastomers. For example, butadiene rubber, which, in an uncured state,typically has a Mooney viscosity (measured according to ASTM D1646-99)greater than about 20, preferably greater than about 30, and morepreferably greater than about 40, may be used in one or more core layersof the golf balls prepared according to the present invention. Inaddition, the compositions of the invention may be incorporated thecore.

Golf Ball Intermediate Layer(s)

An intermediate layer, such as an outer core layer or inner cover layer,i.e., any layer(s) disposed between the inner core and the outer coverof a golf ball may be formed from the compositions of the currentinvention. Such an intermediate layer may be distinguished from a coreor a cover by some difference between the golf ball layers, e.g.,hardness, compression, thickness, etc. An intermediate layer may beused, if desired, with a multilayer cover or a multilayer core, or withboth a multilayer cover and a multilayer core. As with the core, theintermediate layer may also include a plurality of layers.

In one embodiment, the intermediate layer is formed, at least in partfrom the compositions of the invention. For example, an intermediatelayer or inner cover layer having a thickness of about 0.015 inches toabout 0.06 inches may be disposed about a core. In this aspect of theinvention, the core, which has a diameter ranging from about 1.5 inchesto about 1.59 inches, may also be formed from a composition of theinvention or, in the alternative, from a conventional rubbercomposition. The inner ball may be covered by a castable thermoset orinjection moldable thermoplastic material or any of the other covermaterials discussed below. In this aspect of the invention, the covermay have a thickness of about 0.02 inches to about 0.045 inches,preferably about 0.025 inches to about 0.04 inches. The core compressionis about 30 to about 110 atti, preferably about 50 to about 100 atti,and the overall ball compression preferably ranges from about 50 toabout 100 atti.

In another embodiment, the intermediate layer is covered by an innercover layer, either of which may independently be formed from thecompositions of the invention or other material that produces thedesired performance results. For example, a ball of the invention mayinclude a center having a diameter of about 0.5 inches to about 1.30inches and a compression of about 30 to about 110 atti, preferably about50 to about 100 atti. The center may be formed from a composition of theinvention or any of the other core materials previously discussed. Thecore may be covered by an outer core layer to form a core, which alsomay be formed form the compositions of the invention, any of the corematerials discussed above, or castable thermoset materials or injectionmoldable thermoplastic materials. The outer core layer may have athickness of about 0.125 inches to about 0.500 inches. The core may thenbe covered with a casing layer having a thickness of about 0.015 inchesto about 0.06 inches formed from a composition of the invention, acastable thermoset material or an injection moldable thermoplasticmaterial. The outer cover layer, which preferably has a thickness ofabout 0.02 inches to about 0.045 inches, may be formed from a castablethermoset material or an injection moldable thermoplastic material orother suitable cover materials discussed below and known in the art.

When not formed from the compositions of the invention, the intermediatelayer(s) may also be formed, at least in part, from one or morehomopolymeric or copolymeric materials, such as ionomers, primarily orfully non-ionomeric thermoplastic materials, vinyl resins, polyolefins,polyurethanes, polyureas, such as those disclosed in U.S. Pat. No.5,484,870, polyamides, acrylic resins and blends thereof, olefinicthermoplastic rubbers, block copolymers of styrene and butadiene,isoprene or ethylene-butylene rubber, copoly(ether-amide), such asPEBAX, sold by Arkema, Inc. of Philadelphia, Pa., polyphenylene oxideresins or blends thereof, and thermoplastic polyesters.

For example, the intermediate layer may be formed of low acid ionomers,such as those described in U.S. Pat. Nos. 6,506,130 and 6,503,156, highacid ionomers, highly neutralized polymers, such as those disclosed inU.S. Patent Publication Nos. 2001/0018375 and 2001/0019971, or mixturesthereof. The intermediate layer may also be formed from the compositionsas disclosed in U.S. Pat. No. 5,688,191. The entire disclosures of thesepatents and publications are incorporated herein by express referencethereto.

The intermediate layer may also include a wound layer formed from atensioned thread material. The thread may be single-ply or may includetwo or more plies. Suitable thread materials include, but are notlimited to, fiber, glass, carbon, polyether urea, polyether blockcopolymers, polyester urea, polyester block copolymers, syndiotactic- orisotactic-poly(propylene), polyethylene, polyamide, poly(oxymethylene),polyketone, poly(ethylene terephthalate), poly(p-phenyleneterephthalamide), poly(acrylonitrile), diaminodicyclohexylmethane,dodecanedicarboxylic acid, natural rubber, polyisoprene rubber,styrene-butadiene copolymers, styrene-propylene-diene copolymers,another synthetic rubber, or block, graft, random, alternating, brush,multi-arm star, branched, or dendritic copolymers, or mixtures thereof.Those of ordinary skill in the art are aware of the process forproducing thread materials for use with the present invention.

Golf Ball Cover Layer(s)

The cover provides the interface between the ball and a club. Propertiesthat are desirable for the cover are good moldability, high moistureresistance, high abrasion resistance, high impact resistance, high tearstrength, high resilience, and good mold release, among others. Thecover layer may be formed, at least in part, from a composition of theinvention. However, when not formed from the compositions of theinvention, the cover may be formed from one or more homopolymeric orcopolymeric materials as discussed in the section above pertaining tothe intermediate layer. Golf balls according to the invention may alsobe formed having a cover of polyurethane, polyurea, and polybutadienematerials discussed in U.S. Pat. No. 6,835,794.

Layer Formation

The golf balls of the invention may be formed using a variety ofapplication techniques such as compression molding, flip molding,injection molding, retractable pin injection molding, reaction injectionmolding (RIM), liquid injection molding (LIM), casting, vacuum forming,powder coating, flow coating, spin coating, dipping, spraying, and thelike. Conventionally, compression molding and injection molding areapplied to thermoplastic materials, whereas RIM, liquid injectionmolding, and casting are employed on thermoset materials. These andother manufacture methods are disclosed in U.S. Pat. Nos. 6,207,784 and5,484,870, the disclosures of which are incorporated herein by referencein their entirety.

The cores of the invention may be formed by any suitable method known tothose of ordinary skill in art. When the cores are formed from athermoset material, compression molding is a particularly suitablemethod of forming the core. In a thermoplastic core embodiment, on theother hand, the cores may be injection molded. Furthermore, U.S. Pat.Nos. 6,180,040 and 6,180,722 disclose methods of preparing dual coregolf balls. The disclosures of these patents are hereby incorporated byreference in their entirety.

The intermediate layer and/or cover layer may also be formed using anysuitable method known to those of ordinary skill in the art. Forexample, an intermediate layer may be formed by blow molding and coveredwith a dimpled cover layer formed by injection molding, compressionmolding, casting, vacuum forming, powder coating, and the like.

Golf Ball Post-Processing

The golf balls of the present invention may be painted, coated, orsurface treated for further benefits. For example, golf balls may becoated with urethanes, urethane hybrids, ureas, urea hybrids, epoxies,polyesters, acrylics, or combinations thereof in order to obtain anextremely smooth, tack-free surface. If desired, more than one coatinglayer can be used. The coating layer(s) may be applied by any suitablemethod known to those of ordinary skill in the art. In one embodiment,the coating layer(s) is applied to the golf ball cover by an in-moldcoating process, such as described in U.S. Pat. No. 5,849,168, which isincorporated in its entirety by reference herein.

Any of the golf ball layers may be surface treated by conventionalmethods including blasting, mechanical abrasion, corona discharge,plasma treatment, and the like, and combinations thereof. In fact,because low surface energy, or surface tension, is a key feature ofpolysiloxanes, layers formed from the compositions of the invention maybe surface treated according to U.S. Patent Publication No.2003/0199337, the disclosure of which is incorporated in its entirety byreference herein.

Golf Ball Properties

Properties such as core diameter, intermediate layer and cover layerthickness, hardness, and compression can also be altered to affect playcharacteristics such as spin, initial velocity and feel of the presentgolf balls.

Component Dimensions

Dimensions of golf ball components, i.e., thickness and diameter, mayvary depending on the desired properties. For the purposes of theinvention, any layer thickness may be employed. For example, the presentinvention relates to golf balls of any size, although the golf ballpreferably meets USGA standards of size and weight. While “The Rules ofGolf” by the USGA dictate specifications that limit the size of acompetition golf ball to more than 1.680 inches in diameter, golf ballsof any size can be used for leisure golf play. The preferred diameter ofthe golf balls is from about 1.680 inches to about 1.800 inches. Themore preferred diameter is from about 1.680 inches to about 1.760inches. A diameter of from about 1.680 inches (43 mm) to about 1.740inches (44 mm) is most preferred, however diameters anywhere in therange of from 1.700 to about 1.950 inches can be used.

Preferably, the overall diameter of the core and all intermediate layersis about 80 percent to about 98 percent of the overall diameter of thefinished ball. The core may have a diameter ranging from about 0.09inches to about 1.65 inches. In one embodiment, the diameter of the coreof the present invention is about 1.2 inches to about 1.630 inches. Forexample, when part of a two-piece ball according to invention, the coremay have a diameter ranging from about 1.5 inches to about 1.62 inches.In another embodiment, the diameter of the core is about 1.3 inches toabout 1.6 inches, preferably from about 1.39 inches to about 1.6 inches,and more preferably from about 1.5 inches to about 1.6 inches. In yetanother embodiment, the core has a diameter of about 1.55 inches toabout 1.65 inches, preferably about 1.55 inches to about 1.60 inches. Inone embodiment, the core diameter is about 1.59 inches or greater. Inanother embodiment, the diameter of the core is about 1.64 inches orless.

The cover typically has a thickness to provide sufficient strength, goodperformance characteristics, and durability. In one embodiment, thecover thickness is from about 0.02 inches to about 0.12 inches,preferably about 0.1 inches or less. For example, when part of atwo-piece ball according to invention, the cover may have a thicknessranging from about 0.03 inches to about 0.09 inches. In anotherembodiment, the cover thickness is about 0.05 inches or less, preferablyfrom about 0.02 inches to about 0.05 inches, and more preferably about0.02 inches and about 0.045 inches.

The range of thicknesses for an intermediate layer of a golf ball islarge because of the vast possibilities when using an intermediatelayer, i.e., as an outer core layer, an inner cover layer, a woundlayer, a moisture/vapor barrier layer. When used in a golf ball of thepresent invention, the intermediate layer, or inner cover layer, mayhave a thickness about 0.3 inches or less. In one embodiment, thethickness of the intermediate layer is from about 0.002 inches to about0.1 inches, and preferably about 0.01 inches or greater. For example,when part of a three-piece ball or multi-layer ball according to theinvention, the intermediate layer and/or inner cover layer may have athickness ranging from about 0.015 inches to about 0.06 inches. Inanother embodiment, the intermediate layer thickness is about 0.05inches or less, more preferably about 0.01 inches to about 0.045 inches.

Hardness

Solid sphere cores formed of the compositions of the inventionpreferably have a surface hardness of about 20 to 65 Shore D, preferablygreater than about 30 Shore D, and even more preferably greater thanabout 40 Shore D. For example, in one embodiment, a solid sphere formedof the composition of the invention has a surface hardness ranging fromabout 52 to about 65 Shore D.

As such, if additional golf ball layers are formed of the compositions,they also preferably have hardnesses in this range. For example, a golfball layer formed of the composition of the invention may have ahardness greater than about 55 Shore D. In one embodiment, the hardnessis about 60 Shore D or greater. In another embodiment, additional golfball layers are formed of alternative compositions with hardness rangesfrom about 35 Shore D to about 50 Shore D, preferably from about 40Shore D to about 50 Shore D. Because the compositions of the inventionmay be used in any layer of a golf ball, the golf ball construction,physical properties, and resulting performance may vary greatlydepending on the layer(s) of the ball that include the compositions ofthe invention.

The intermediate layer(s) of the present invention may also vary inhardness depending on the specific construction of the ball. In oneembodiment, the hardness of the intermediate layer is about 30 Shore Dor greater. In another embodiment, the hardness of the intermediatelayer is about 90 Shore D or less, preferably about 80 Shore D or less,and more preferably about 70 Shore D or less. For example, when anintermediate layer is formed from the compositions of the invention, thehardness of the intermediate layer may be about 55 Shore D or greater,preferably ranging from about 55 Shore D to about 65 Shore D. In yetanother embodiment, the hardness of the intermediate layer is about 50Shore D or less, preferably from about 35 Shore D to about 55 Shore D.The intermediate layer may also be about 65 Shore D or greater. Forexample, a golf ball of the invention may include an inner cover formedfrom an ionomer having a hardness of about 60 Shore D to about 75 ShoreD.

As with the core and intermediate layers, the cover hardness may varydepending on the construction and desired characteristics of the golfball. The ratio of cover hardness to inner ball hardness is a primaryvariable used to control the aerodynamics of a ball and, in particular,the spin of a ball. In general, the harder the inner ball, the greaterthe driver spin and the softer the cover, the greater the driver spin.

For example, when the intermediate layer is intended to be the hardestpoint in the ball, e.g., about 60 Shore D to about 75 Shore D, the covermaterial may have a hardness of about 20 Shore D or greater, preferablyabout 25 Shore D or greater, and more preferably about 30 Shore D orgreater, as measured on the slab. In another embodiment, the coveritself has a hardness of about 30 Shore D or greater. In particular, thecover may be from about 30 Shore D to about 70 Shore D. In oneembodiment, the cover has a hardness of about 40 Shore D to about 65Shore D, and in another embodiment, about 40 Shore to about 55 Shore D.In another aspect of the invention, the cover has a hardness less thanabout 45 Shore D, preferably less than about 40 Shore D, and morepreferably about 25 Shore D to about 40 Shore D. In one embodiment, thecover has a hardness from about 30 Shore D to about 40 Shore D.

Compression

Compression is an important factor in golf ball design. For example, thecompression of the core can affect the ball's spin rate off the driverand the feel. In fact, the compositions and methods of the presentinvention result in a rigid inner ball that ultimately results in anoverall harder ball. The harder the overall ball, the less deformed itbecomes upon striking, and the faster it breaks away from the golf club.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, “compression” refers to Atti compression and is measuredaccording to a known procedure, using an Atti compression test device,wherein a piston is used to compress a ball against a spring. The travelof the piston is fixed and the deflection of the spring is measured. Themeasurement of the deflection of the spring does not begin with itscontact with the ball; rather, there is an offset of approximately thefirst 1.25 mm (0.05 inches) of the spring's deflection. Very lowstiffness cores will not cause the spring to deflect by more than 1.25mm and therefore have a zero compression measurement. The Atticompression tester is designed to measure objects having a diameter of42.7 mm (1.68 inches); thus, smaller objects, such as golf ball cores,must be shimmed to a total height of 42.7 mm to obtain an accuratereading. Conversion from Atti compression to Riehle (cores), Riehle(balls), 100 kg deflection, 130-10 kg deflection or effective moduluscan be carried out according to the formulas given in J. Dalton.

The Atti compression of the core, or portion of the core, of golf ballsprepared according to the invention may range from about 60 to about 120atti, preferably about 65 to about 115 atti, and most preferably 70 to110 atti. In one embodiment, the core compression is less than about 80,preferably less than about 75.

Coefficient of Restitution

The coefficient of restitution or COR of a golf ball is a measure of theamount of energy lost when two objects collide. The COR of a golf ballindicates its ability to rebound and accounts for the spring-like feelof the ball after striking. As used herein, the term “coefficient ofrestitution” (COR) is calculated by dividing the rebound velocity of thegolf ball by the incoming velocity when a golf ball is shot out of anair cannon. The COR testing is conducted over a range of incomingvelocities and determined at an inbound velocity of 125 ft/s.

The present invention contemplates golf balls having CORs from about0.700 to about 0.850 at an inbound velocity of about 125 ft/sec. In oneembodiment, the COR is about 0.750 or greater, preferably about 0.780 orgreater. In another embodiment, the ball has a COR of about 0.800 orgreater. In yet another embodiment, the COR of the balls of theinvention is about 0.800 to about 0.815.

Solid spheres (1.55 inches) formed of the compositions of the inventionmay have a COR of at least about 0.790, preferably at least about 0.800.For example, the COR of solid spheres formed from the compositions ofthe invention ranges from about 0.810 to about 0.830. In one embodiment,a solid sphere formed from the composition of the invention has a COR ofabout 0.800 to about 0.825. In another embodiment, the COR of the solidsphere ranges from about 0.805 to about 0.815.

EXAMPLES

The following non-limiting examples are merely illustrative of thepreferred embodiments of the present invention, and are not to beconstrued as limiting the invention, the scope of which is defined bythe appended claims.

Example 1

A golf ball according to the invention may be formed with a core orinner layer that is formed from a composition that includes a blend of alinear Nd-BR having a SV/MV ratio of about 5.5 to about 7.0 and abranched Nd-BR having a SV/MV ratio of about 2.0 to about 4.0. The innerball may be covered with a cover formed from a thermoplastic orthermoset material.

Example 2

A golf ball according to the invention may be formed with a core that isformed from a composition that includes a blend of a linear Nd-BR havinga SV/MV ratio of about 5.5 to about 7.0 and a branched Nd-BR having aSV/MV ratio of about 3.6 to about 3.8. The SV may range from about 159to about 165 and the MV may be about 44. The inner ball may be coveredwith a cover formed from a thermoplastic or thermoset material.

Example 3

A golf ball according to the invention may be formed with a core that isformed from a composition that includes a blend of a linear Nd-BR havinga SV/MV ratio of about 5.9 to about 6.6 and a branched Nd-BR having a MVof 44, a SV of 159, and a SV/MV ratio of 3.6.

Example 4

A golf ball according to the invention may be formed with a core that isformed from a composition that includes a blend of a linear Nd-BR havinga SV/MV ratio of about 5.9 to about 6.6 and a branched Nd-BR having a MVof 44, a SV of 165, and a SV/MV ratio of 3.8.

Example 5

A golf ball according to the invention may be formed with a core that isformed from a composition that includes a blend of a linear Nd-BR havinga SV/MV ratio of about 5.9 to about 6.6 and a branched Nd-BR having a MVof 44, a SV of 160, and a SV/MV ratio of 3.6.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Furthermore, when numerical ranges ofvarying scope are set forth herein, it is contemplated that anycombination of these values inclusive of the recited values may be used.

The invention described and claimed herein is not to be limited in scopeby the specific embodiments herein disclosed, since these embodimentsare intended as illustrations of several aspects of the invention. Anyequivalent embodiments are intended to be within the scope of thisinvention. For example, the compositions of the invention may also beused in golf equipment such as putter inserts, golf club heads andportions thereof, golf shoe portions, and golf bag portions. Indeed,various modifications of the invention in addition to those shown anddescribed herein will become apparent to those skilled in the art fromthe foregoing description. Such modifications are also intended to fallwithin the scope of the appended claims. All patents and patentapplications cited in the foregoing text are expressly incorporateherein by reference in their entirety.

What is claimed is:
 1. A golf ball comprising a core and a cover,wherein the core is formed from a blend comprising: a linearpolybutadiene formed with a neodymium catalyst having a firstpolydispersity and a first Mooney viscosity of from about 30 to about100; and a branched polybutadiene formed with a neodymium catalysthaving a second polydispersity greater than the first polydispersity anda second Mooney viscosity of from about 30 to about 75, wherein thesecond Mooney viscosity is less than the first Mooney viscosity.
 2. Thegolf ball of claim 1, wherein the linear polybutadiene has a higherMooney Stress Relaxation than the branched polybutadiene.
 3. The golfball of claim 1, wherein the second Mooney viscosity is of from about 35to about
 50. 4. The golf ball of claim 3, wherein the second Mooneyviscosity is about 40 to about
 45. 5. The golf ball of claim 1, whereinthe branched polybutadiene has a solution viscosity to Mooney Viscosityratio of about 3.0 to about 4.0.
 6. The golf ball of claim 5, whereinthe branched polybutadiene has a solution viscosity to Mooney Viscosityratio of about 3.6 to about 3.8.
 7. The golf ball of claim 1, whereinthe linear polybutadiene has a solution viscosity to Mooney Viscosityratio of greater than about
 5. 8. The golf ball of claim 1, wherein thesolution viscosity to Mooney Viscosity ratio of the linear polybutadieneis at least about 2 times greater than the solution viscosity to MooneyViscosity ratio of the branched polybutadiene.
 9. The golf ball of claim1, further comprising an intermediate layer disposed between the coverand the core.
 10. The golf ball of claim 1, wherein the blend furthercomprises cobalt-, lithium-, titanium-, or nickel-catalyzedpolybutadienes.
 11. A golf ball comprising a core, a cover, and anintermediate layer disposed between the cover and the core, wherein aportion of the golf ball is formed from a blend comprising: a linearpolybutadiene formed with a neodymium catalyst having a firstpolydispersity and a first Mooney viscosity; and a branchedpolybutadiene formed with a neodymium catalyst having a secondpolydispersity greater than the first polydispersity and a second Mooneyviscosity less than the first Mooney viscosity, wherein the secondpolydispersity is greater than about 2, and wherein the second Mooneyviscosity is of from about 35 to about
 50. 12. The golf ball of claim11, wherein the linear polybutadiene has a first Mooney StressRelaxation and the branched polybutadiene has a second Mooney StressRelaxation, and wherein the second Mooney Stress Relaxation is less thanthe first Mooney Stress Relaxation.
 13. The golf ball of claim 11,wherein the first polydispersity is less than about
 3. 14. The golf ballof claim 11, wherein the first Mooney viscosity is of from about 30 toabout
 100. 15. The golf ball of claim 11, wherein the core comprises acenter and at least one outer core layer, and wherein at least one ofthe center or the outer core comprises the blend.
 16. The golf ball ofclaim 11, wherein the cover comprises polyurethane, polyurea, or acombination thereof.
 17. A golf ball comprising a core and a cover,wherein the core comprises a blend comprising: a linear polybutadieneformed with a neodymium catalyst having a first polydispersity and afirst solution viscosity to Mooney Viscosity ratio; and a branchedpolybutadiene formed with a neodymium catalyst having a secondpolydispersity greater than the first polydispersity and a secondsolution viscosity to Mooney Viscosity ratio less than the firstsolution viscosity to Mooney Viscosity ratio, and wherein the secondsolution viscosity to Mooney Viscosity ratio ranges from about 3 toabout 4 and the first solution viscosity to Mooney Viscosity ratioranges from about 5 to about
 12. 18. The golf ball of claim 17, whereinthe cover comprises a thermoset material.
 19. The golf ball of claim 17,further comprising an intermediate layer formed from a thermoplasticmaterial.
 20. The golf ball of claim 17, wherein the ratio of weightpercentage of the branched polybutadiene to the linear polybutadiene isat least about 60:40.